1. Field of the Invention
This invention relates to an improvement of an apparatus for morphological observation of a sample, such as a scanning electron microscope (SEM) or the transmission electron microscope (TEM).
2. Prior Art
Heretofore, there have been known apparatus for observing the surface structure of a sample, such as a scanning electron microscope or a transmission electron microscope. For example, the scanning electron microscope scans an electron beam on a sample surface. The scanning electron microscope detects a secondary electron or a backscattered electron. The apparatus for morphological observation of a sample as the scanning electron microscope forms dark and bright morphological image signals (shading image signals) in accordance with detection signals of the electron detector. The morphological image is indicative of that of the sample.
When bombarded with the electron ray, some samples are stimulated at a particular part thereof to emit a photoluminescence. There is also known an apparatus for morphological observation a sample of a scanning electron microscope which receives a photoluminescence stimulated by an electron ray irradiated to a sample and displays the illuminated part (i.e., stimulated part) of the sample in color.
As shown in FIGS. 4 and 5, in the conventional apparatus for morphological observation of a sample of the scanning electron microscope of this type, a morphological image 1 obtained by bombarding charged particles and a color image 2 obtained by a photoluminescence are separately taken in photographs, and the morphological image 1 and the color image 2 are placed side by side for comparison in order to identify the illumination part of the sample. FIG. 4 shows a morphological image of a mitochondria, and FIG. 5 shows a luminous part thereof.
Therefore, it is difficult to obtain a corresponding relation between each part of the morphological image 1 of the sample and the luminous part of the sample in such cases that the morphological image 1 is complicated in shape and the photo-luminescence is faint. Particularly, if the power is increased when the sample is a biological material, the chemical bond of polymer is disconnected by bombardment with the electron ray and as a result, discoloration occurs. Moreover, the photoluminescence becomes extremely faint, and the luminous area is difficult to be identified.